TiO2-modulated tetra (4-carboxyphenyl) porphyrin/perylene diimide organic Z-scheme nano-heterojunctions for efficiently visible-light catalytic CO2 reduction

Developing efficient Z-scheme heterojunctions with wide visible-light responsive perylene diimide (PDI) is highly desired for CO2 conversion, while the effective charge transfer and separation are crucial. Herein, TiO2-modulated tetra(4-carboxyphenyl)porphyrin/perylene diimide (T-TP/PDI) organic nano-heterojunctions have been fabricated for CO2 reduction, in which TP and PDI are first assembled via pi-pi interactions between their similar 2D conjugate structures, and then the TiO2 nanoparticles (ca. 10 nm) are anchored as an energy platform through the carboxyl groups on TP. The optimal one exhibits a similar to 10-fold enhancement in photocatalytic activity compared with the pristine PDI. Based on the time-resolved surface photovoltage responses, electron paramagnetic resonance signals, in situ diffuse reflectance infrared Fourier transform spectra and the amount evaluation of H2O2 as the water-oxidation intermediate, it is suggested that the exceptional photoactivity be ascribed to the accelerated charge transfer and separation resulting from the constructed Z-scheme nano-heterojunctions with intimate interfacial interactions and the introduced energy platform TiO2 oriented towards largely inhibiting the type-II charge transfer pathway. This work diversifies the strategies for constructing efficient organic Z-scheme heterojunctions, and provides insight into interface correlation among components.